Hydraulic steering arrangement

ABSTRACT

A hydraulic steering arrangement, having a steering value, which connects a steering motor with a pump, and which has a slide with two front sides, the slide being adjustable by means of a pressure fluid both through a hydraulic steering unit with a steering hand wheel and through an electro hydraulic steering unit with a control pressure generator. The two steering units have working connections and the front sides of the slide are connected with shuttle valves, each of which is connected with hydraulic steering unit on the one side and with the electro hydraulic steering unit on the other side. A valve arrangement connects the working connection of both steering units, which has the highest pressure, with one front side of the slide, and the working connection of both steering units, which has the lowest pressure, with the other front side of the slide.

BACKGROUND OF THE INVENTION

The invention concerns a hydraulic steering arrangement, having asteering valve, which connects a steering motor with a pump, and whichhas a slide with two front sides, the slide being adjustable by means ofa pressure fluid both through a hydraulic steering unit with a steeringhand wheel and through an electro hydraulic steering unit with a controlpressure generator, the two steering units having working connectionsand the front sides of the slide being connected with shuttle valves,each of which being connected with the hydraulic steering unit on theone side and with the electro hydraulic steering unit on the other side.

A steering arrangement of this kind is known, for example, from thepost-published German patent application 199 31 143.9. In this document,each front side of the slide is connected direct in series with ashuttle valve. Each of the two shuttle valves is acted upon by a workingpressure of the hydraulic steering unit and a working pressure of theelectro hydraulic steering unit. In this connection, each front side ofthe slide is acted upon by the higher working pressure available at itsseries-connected shuttle valve. Thus, the steering valve is operableboth via the hydraulic and the electro hydraulic steering unit. As thehydraulic steering unit can build up the largest working pressure of thesteering arrangement, the hydraulic steering unit can at any time beused to control the vehicle. In this connection, the reaction time ofthe steering unit depends on the pressures, which act on both frontsides of the slide.

SUMMARY OF THE INVENTION

The invention is based on the task of reducing the reaction time.

In a hydraulic steering arrangement as mentioned in the introduction,this task is solved in that a valve arrangement is provided, which,during normal operation, connects the working connection of bothsteering units, which has the highest pressure, with one front side ofthe slide, and the working connection of both steering units, which hasthe lowest pressure, with the other front side of the slide.

Thus, it is ensured that during normal operation of the hydraulicsteering unit the highest available pressure always works together withthe lowest pressure at the steering valve, meaning that the largestpressure difference acts across the slide. During normal operation, thelowest pressure comes from a tank connection of the hydraulic steeringunit, assuming that both working connections R, L of the hydraulicsteering unit have the same pressure, when being connected at the sametime with the tank connection T. During normal operation, this is thecase when only the electro hydraulic steering unit is activated. In thisconnection, the tank connection is connected with a tank or anotherpressure sink. During normal operation this gives the maximum possiblepressure difference and the shortest possible reaction time.

Preferably, the valve arrangement has two branches, and in each branchone working connection of the hydraulic steering unit or one workingconnection of the electro hydraulic steering unit is connectable withone front side of the slide. Each of the two branches thus combines twopaths, which are acted upon by pressure from the various steering units.This simple arrangement of the pressure paths reduces the costs.Additionally, the arrangement of the two pressure paths of a steeringunit in different branches provides an improved working reliability ofthe steering arrangement.

Further, it is preferred that each branch has one path for a higher andone path for a lower of two working pressures. Thus, a predeterminedpath is allocated to the individual pressures according to their sizeand relative to the other pressure of the same path, which enablessimplified switching arrangements and thus also a more reliableswitching operation.

It is particularly preferred that each branch has at least one crossconnection to the other branch, through which an adjustment pressure canact upon a valve of the other branch. This increases the number ofswitching functions of the valve arrangement, which provides anoptimised pressure admission of the steering valve.

It is advantageous that the hydraulic steering unit supplies a higherpressure than the electro hydraulic steering unit. This ensures that thevehicle can at any time be steered by means of a manual operation of thehydraulic steering unit. This ensures a high reliability of the steeringarrangement.

Further, it is advantageous that each of the two branches has at leasttwo three/two-way valves and at least one shuttle valve. These valvesprovide a large number of switching opportunities, the simple embodimentof the individual valves reducing the costs and ensuring a stableoperation.

Preferably, the first three/two-way valve of a branch, seen from asteering unit, is controlled so that it is penetrable by the lower ofthe two pressures ruling at the working connections of the steeringunit. Thus, the lower pressure of the two branches is already branchedat an early stage. This ensures that it is with a high reliabilityavailable in both branches, to act upon the front sides of the slide,each being connected in series with one of the two branches.

Additionally, it is preferred that the first three/two-way valve of eachbranch has two inlet connections, each connected with a steering unit,and an outlet, which is connected with an inlet connection of adownstream-connected second three/two-way valve, the first three/two-wayvalve being operable via adjustment connections, which again areconnected with one of the connections between the inlet connections andthe steering units. This simple embodiment of the valve enables aninexpensive and reliable switching of two ruling pressures in such a waythat the lower pressure is passed on.

It is advantageous that the shuttle valve of a branch has two workingconnections, one being connected with the hydraulic steering unit, onewith the electro hydraulic steering unit. The shuttle valve has a verysimple embodiment and is penetrable by the higher of two pressures.Thus, the shuttle valve arranged here ensures lower costs and a reliablepassing on of the higher of the ruling pressures.

It is advantageous that the outlet of the shuttle valve is connectedwith an inlet connection and an adjustment connection of the secondthree/two-way valve and with the cross connection. The consequence ofthis is that the highest pressure ruling in any of the two branches isnow available as adjustment pressure in both branches, thus permittingan optimisation of the switching processes.

Further, it is advantageous that the cross connection connects theoutlet of the shuttle valve of the one branch with an adjustmentconnection of the second three/two-way valve of the other branch. Thispermits that in an operation reliable and cost effective way the highestpressure ruling in the other branch is always acting as adjustmentpressure on the two second three/two-way valves.

It is favourable that the second three/two-way valve of a branch, seenfrom the direction of a steering unit, is adjustable via an adjustmentconnection, which is connected with one of the cross connections, andvia an adjustment connection, which is connected with the outlet of theshuttle valve of the branch, and has an outlet, which is connected witha front side of the slide. This arrangement makes it possible that theconnection of a branch with the downstream-connected front side of theslide is operable by means of pressures from both branches. Thus, thepressure application of the valve can be optimised.

Further, it is advantageous that the highest of the pressures, which arepassed on by the two shuttle valves of the valve arrangement, operatesthe second three/two-way valves of the two branches. Thus, the twoconnections between the branches and their downstream-connected frontside of the slide are operated by the highest available pressure. Thiscauses a simplified and reliable adjustment of both switching processes.

It is advantageous that each of the second three/two-way valves isoperated so that the one of the second three/two-way valves of bothbranches being acted upon by the highest of the pressures passed on bythe two shuttle valves of the valve arrangement, passes on this pressureto the one front side of the slide, and the other second three/two-wayvalve passes on the lower of the pressures, which rules at the two inletconnections, to the other front side of the slide. Thus, it is ensuredthat between the two front sides of the slide, which are acted upon byone of the pressures of the series-connected branch, the highestpossible pressure difference is ruling. For the normal operation, thismeans that on one side the steering valve is connected with the workingpressure of a tank connection of the hydraulic steering unit and on theother side with the working pressure of the pump connection of theactivated steering unit. In this way the shortest possible reaction timefor the steering is obtained.

BRIEF DESCRIPTION OF THE DRAWING

In the following, the invention is described in detail on the basis of apreferred embodiment in connection with the drawing, showing:

Only FIGURE a schematic view of a hydraulic steering unit

DESCRIPTION OF THE PREFERRED EMBODIMENT

A hydraulic steering arrangement 1 has a steering valve 2 with a slide 3and a hydraulic steering unit 4 with a steering handwheel 5 and anelectro hydraulic steering unit 6 with a control pressure generator. Thehydraulic steering unit 4 is a traditional steering unit with twomutually rotatable slides. In this connection, the steering hand-wheelrotates one of the two slides, thus releasing a path from a pumpconnection P to one of the working connections 7 (L, R), while the otherworking connection 7 (R, L) is connected with a tank connection T.

Further, the hydraulic steering arrangement has a valve arrangement 10consisting of shuttle valves and three/two-way valves. The outlet of thesteering valve 2 is connected with a steering motor, which operates thesteered wheels of a vehicle (not shown).

The hydraulic pressures, which are used for the operation of thesteering valve 2, can be produced in two different ways. Firstly, thehydraulic pressures are produced by the control pressure generator ofthe electro hydraulic steering unit 6 and supplied to two front sides 8of the slide 3 of the steering valve 2 via the valve arrangement 10.However, the hydraulic pressures can also be produced through anactivation of the hydraulic steering unit 4. The working connections 7of the hydraulic steering unit 4 can also be connected with the frontsides 8 of the slide 3 via the valve arrangement 10.

The valve arrangement 10 has two branches 11, each of which having twothree/two-way valves 13 a, 13 b and a shuttle valve 9. Each branch 11 isacted upon by a pressure from each of the two steering units. In theoperation example of the embodiment according to the Fig., the leftbranch 11 is connected with the working connection 7 of the hydraulicsteering unit 4, which is acted upon by the tank connection T.Additionally, the left branch 11 is connected with a working connection7 of the electro hydraulic steering unit. The second working connection7 of the electro hydraulic steering unit 6 is connected with the rightbranch 11 of the valve arrangement, together with the second workingconnection of the hydraulic steering unit, which is acted upon by thepump connection P.

Seen from the direction of a steering unit, firstly the firstthree/two-way valve 13 a of each steering unit is acted upon by apressure from both of the steering units 4, 6. Both connections betweenthe two steering units and a first three/two-way valve 13 a haveadditional connections with its two adjustment connections 16. Bothworking pressures ruling at two inlet connections 14 of the respectivefirst three/two-way valves 13 a thus at the same time also act upon thethree/two-way valve 13 a as adjustment pressure via the adjustmentconnections 16. For this purpose, the first three/two-way valve 13 a ofboth branches 11 is made so as to be penetrable for the lower of the twoworking pressures ruling. The lower working pressure is now passed on toa downstream-connected three/two-way valve 13 b via the outlet 15.

Next to the first three/two-way valve 13 a, the two working connections7 of both steering units, which act upon a branch with working pressure,are also connected with the shuttle valve 9 of the branch 11 inquestion. The outlet 15 of this valve 9 is connected with an inletconnection 14 and an adjustment connection 16 of the secondthree/two-way valve 13 b of each individual branch 11 and via a crossconnection 12 with an adjustment connection 16 of the secondthree/two-way valve 13 b of the other branch 11. Thus, the pressurepassed on by a shuttle valve 9 is available as both working pressure andadjustment pressure for the downstream-connected second three/two-wayvalve 13 b of one of the branches and as adjustment pressure for thesecond three/two-way valve 13 b of the other branch.

Through the cross connections 12, a comparison of the respective highestpressures of both branches 11, which are passed on by the shuttle valves9 is possible. The two second three/two-way valves 13 b are connected sothat in the branch, in which the highest of the pressures, which arepassed on by the shuttle valves 9, is available, this pressure is alsopassed on by the second three/two-way valve 13 b of the same branch tothe downstream-connected front side 8 of the slide 3. As explained inthe following, consequently, during normal operation, at least one frontside 8 of the slide is connected with a working connection of thehydraulic steering unit.

The pressure admission on the hydraulic steering arrangement is made sothat the hydraulic steering unit 4 can at any time pass on a higherpressure than the electro hydraulic steering unit 6. Additionally,experience shows that the pressure in the lines of the electro hydraulicsteering unit are built up to the size of 4 to 5 bar due to a controlloop, when the steering unit is not activated.

An operation of the steering handwheel 5 will thus, during normaloperation, cause that both the highest and the lowest working pressureof the valve arrangement are supplied by the hydraulic steering unit 4.In this connection, the highest pressure, which comes from the pumpconnection of the hydraulic steering unit 4, acts in one branch 11, andthe lowest working pressure, which comes from the tank connection T ofthe hydraulic steering unit 4 acts in the other branch 11. On the otherhand, on an operation of the steering handwheel during normal operation,the working pressures of the electro hydraulic steering unit 6 will havea size, which lies between the working pressure of the tank connection Tand the pump connection P of the hydraulic steering unit 4. Thus, thetwo second three/two-way valves 13 b of the valve arrangement 10 areoperated by the highest pressure of the pump connection of the hydraulicsteering unit in such a way that it is passed on to the one front side 8of the slide 3, whereas the lowest pressure, which comes from the tankconnection T of the hydraulic steering unit 4, is connected with theother front side 8 of the slide 3 via the other branch 11.

When, however, not the hydraulic steering unit 4, but the electrohydraulic steering unit 6 is operated, then the latter can build up thehighest working pressure. Both working connections 7 of the hydraulicsteering unit 4 are now connected with the tank and have the lowestworking pressure. Consequently, the highest working pressure of theelectro hydraulic steering unit 6 operates the two second three/two-wayvalves 13 b of the valve arrangement 10 in such a way that this highestworking pressure of the electro hydraulic steering unit 6 is connectedwith a front side 8 of the slide 3 via a branch 11. The lowest workingpressure, which comes from the working connection 7 of the hydraulicsteering unit 4, which acts upon the other branch 11, is connected withthe other front side 8 of the slide 3.

In case that during a control via the electro hydraulic steering unit 6,the hydraulic steering unit 4 is also operated, the hydraulic steeringunit 4 can now build up a higher working pressure than the electrohydraulic steering unit 6. The two second three/two-way valves 13 b arethus operated in such a way that the branch with the highest workingpressure of the hydraulic steering unit 4 is connected with one of thefront sides of the slide 3 in such a way that the highest workingpressure of the hydraulic steering unit 4 acts upon thedownstream-connected front side 8 of the slide 3. Via the other branch11, on the other hand, the lowest working pressure available is led tothe other front side 8 of the slide 3.

What is claimed is:
 1. Hydraulic steering arragement having a steeringvalve which connects a steering motor with a pump, the steering valvehaving a slide with two front sides, the slide being adjustable by meansof a pressure fluid both through a hydraulic steering unit having asteering hand wheel and through an electro hydraulic steering unithaving a control pressure generator, the two steering units havingworking connections and the front side of the slide being connected toshuttle valves, each of which being connected with the hydraulicsteering unit on one side and with the electro hydraulic steering uniton a second side, and including a valve arrangement, which, duringnormal operation, connects the working connection of both steeringunits, which has highest pressure, with one front side of the slide, andthe working connection of both steering units, which has lowestpressure, with the other front side of the slide.
 2. Steeringarrangement according to claim 1, in which the valve arrangement has twobranches, and in each branch one working connection of the hydraulicsteering unit or one working connection of the electro hydraulicsteering unit is connectable with one front side of the slide. 3.Steering arrangement according to claim 2, in which each branch has onepath for a higher and one path for a lower of two working pressures. 4.Steering arrangement according to claim 2, in which each branch has atleast one cross connection to the other branch, through which anadjustment pressure acts upon a valve of the other branch.
 5. Steeringarrangement according to claim 2, in which each of the two branches hasat least two three/two-way valves and at least one shuttle valve. 6.Steering arrangement according to claim 5, in which the firstthree/two-way valve of a branch, downstream of a steering unit, iscontrolled so that it is penetrable by the lower of the two pressuresruling at the working connections of the steering unit.
 7. Steeringarrangement according to claim 6, in which the first three/two-way valveof each branch has two inlet connections, each connected with a steeringunit, and an outlet, which is connected with an inlet connection of adownstream-connected second three/two-way valve, the first three/two-wayvalve being operable via adjustment connections, which are connectedwith one of the connections between the inlet connections and thesteering units.
 8. Steering arrangement according to claim 7, in whichthe shuttle valve of a branch has two working connections, one beingconnected with the hydraulic steering unit, one being connected with theelectro hydraulic steering unit.
 9. Steering arrangement according toclaim 8, in which the outlet of the shuttle valve is connected with aninlet and an adjustment connection of the second three/two-way valve andwith a cross connection.
 10. Steering arrangement according to claim 9,in which the cross connection connects the outlet of the shuttle valveof the one branch with an adjustment connection of the secondthree/two-way valve of the other branch.
 11. Steering arrangementaccording to claim 5, in which the second three/two-way valve of abranch, downstream of a steering unit, is adjustable via an adjustmentconnection, which is connected with a cross connection, and via anadjustment connection, which is connected with an outlet of a shuttlevalve of the branch, and has an outlet, which is connected with a frontside of the slide.
 12. Steering arrangement according to claim 5, inwhich the highest of the pressures, which are passed on by the twoshuttle valves of the valve arrangement, operates the secondthree/two-way valves of the two branches.
 13. Steering arrangementaccording to claim 12, in which each of the second three/two-way valvesis operated so that one of the second three/two-way vales of boothbranched being acted upon by the highest of the pressures passed on bythe two shuttle valves of the valve arrangement, passes on this pressureto the one front side of the slide, and the other second three/two-wayvalve passes on the lower of the pressures, which rules inletconnections of the three/two-way valves, to the other front side of theslide.
 14. Steering arrangement according to claim 1, in which thehydraulic steering unit supplies a higher pressure than the electrohydraulic steering unit.